Observing Strategies

The gaps between the three detectors in both GMOS cause gaps in the spectral coverage,
see the data examples. The size of the gaps in wavelength space
depends on the grating used, but is typically a few
nanometers. If continuous spectral coverage is essential for your program, consider
using two configurations of the grating with central wavelengths 3-5 nm different.

The width of each fiber in the IFU is only 5 unbinned pixels. Thus, it is recommended
to always have the Y-direction of the detectors unbinned. The spectral resolution of
the IFU is equivalent to a slit with 0.31 arcsec width (3.88 unbinned pixels for Hamamatsu, 4.26 unbinned pixels for e2v), thus you
may consider binning in the spectral direction if your object is very faint.

You will have to decide if your science targets are best observed in IFU 2-slit
mode or IFU 1-slit mode. The 2-slit mode gives you a larger field on the sky
at the expense of spectral coverage. The 1-slit mode gives you larger spectral
coverage, but half the field of view on the sky compared to the 2-slit mode.
In 2-slit mode you will have to use one of the color filters in order to avoid
overlap between the spectra, see the spectral overlap page
for details. In 1-slit mode you may have to use a filter to avoid 2nd order
contamination.

In 1-slit mode the central wavelength you specify will be interpreted as the
desired wavelength at the center of the detector array. In 2-slit mode, the
central wavelength you specify will be the wavelength at the location of the
two pseudo-slits.

If your science target cannot be detected in imaging mode in one of the GMOS filters
in about 5 min of exposure time, you will need to supply coordinates for a nearby
brighter target (R<19 mag. and preferably a point source) and accurate
offsets between that brighter target and your science target. The accuracy of
blind offsetting is better than 0.1 arcsec for offsets less than 20 arcsec.
For the blind offsetting to work it is essential that the same guide star can be
reached for the bright object and the science target.

If your science target is fainter than about R=18, you will have to supply a
finding chart at the time of Phase II submission.

Are the Baseline Calibrations sufficient for your
program? If you need accurate
telluric line removal, you will need to add telluric standard stars to your program.
If you need radial velocity standards, these need to be added to your program.
Also if you need very accurate velocity calibration and you are observing in the
blue where not many skylines are available from which to bootstrap your daytime
CuAr, you may need to request CuAr calibrations be taken on the sky with your
science observation.

IFU Target Acquisition and Observation Definition

IFU Target acquisition is done by taking a GMOS image of the field using the
sub-region of the CCDs that contains the IFU fields. An IRAF task in
the Gemini package can overlay the IFU fields on the image and calculate
the offsets to the desired position in the IFU field-of-view. Another task does rapid IFU image reconstruction to verify the placement
of the target in the IFU. The following information is needed to define an
IFU observation:

One-slit or two-slit mode. If in one-slit mode, then one can
choose which slit to use (IFU Right Slit (Red) recommended for both GMOS-N and GMOS-S).

Coordinate to be centered in the desired IFU field.

Position angle (PA) to track. Note that the long axis of the
Object field changes by 90 degrees between one and two-slit modes.